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    SubjectRe: [linux-pm] Freezer: Don't count threads waiting for frozen filesystems.
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    On Tue, 28 Oct 2008, Nigel Cunningham wrote:
    > The answer is to freeze the fuse filesystems first, stopping new
    > requests (freezing the processes making them) before they are passed on
    > to userspace and allowing existing requests to complete or freeze. Once
    > that is done, the userspace fuse processes will be idle, at least as far
    > as fuse activity is concerned. After fuse activity is stopped, userspace
    > can be frozen without worrying about what processes are fuse and what
    > aren't. This is what my patch implements so far.

    OK.

    > To deal with requests that are already in progress, I'd suggest three
    > possibilities, in the order I think they should be preferred.
    >
    > 1) Use wait_event_freezeable[_timeout] in fuse code. Probably preferable
    > to #2, but I thought of it later :)
    >
    > 2) Use freezer_do_not_count as part of FUSE_MIGHT_FREEZE (resetting
    > before exiting the callers, of course). If the request doesn't complete
    > during the freezing period, it must be because the userspace thread was
    > already frozen. If the request does complete, we're counted again during
    > the normal freezing of userspace that follows the freezing of
    > filesystems.
    >
    > 3) Adding a means to check whether processes being frozen are fuse
    > requests. The code could then wait for fc->num_waiting - (say)
    > fc->num_frozen == 0.

    Yup, these fix the freezing of tasks which have outstanding fuse
    requests.

    However it does not fix the freezing of tasks which are waiting for
    VFS locks (i.e. inode->i_mutex) held by the outstanding fuse requests.
    This is the tricky part...

    Miklos


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